Such safety systems are used to outfit motor vehicles not having any roof structure—like convertibles—or whose roof structure does not afford sufficient protection to the passengers in event of a rollover. Dynamic systems with a roll bar which can be moved from a position of rest to a protection position are used when rigid roll bars are not desired due to visual appearance.
As with the activation of air bags, pyrotechnical actuators are used to release the holding device: after a “rollover signal” has been generated by means of appropriate sensors, they are electronically actuated and ignited to produce a mechanical adjustment movement. Pyrotechnical actuators are preferable for use, because with them the “rollover signal” can be very quickly converted into a triggering adjustment movement so that the roll bar can be brought into the protection position swiftly before the rollover is completed.
The igniting of the pyrotechnical actuator results in the catch element of the holding device being abruptly disengaged, releasing the driving force for the movement of the roll bar.
However, it has been found that rebound effects may occur after the abrupt acceleration of the catch element, because the distance available to the catch element after the point of release is limited. The limitation can be desirable for design reasons, or necessitated by the installation process.
The accelerated catch element can then bounce back toward its starting position and again produce a catching effect before the roll bar with its much greater inertia than that of the catch element is sufficiently accelerated and has moved far enough toward the protection position so that the catch element can no longer become engaged. The reaction times between generation of the “rollover signal” and the movement of the roll bar at least to a position no longer catchable are in the range of 15 ms.
Furthermore, one must consider that unforeseeable acceleration forces will act on all elements of the system during a rollover and may substantially alter the time course of the process—as compared to what was found during testing.
Hence, the problem is to avoid a rebounding of the catch element that is abruptly accelerated to release the holding device after it impacts against a structural element bordering on its exit path.